The present invention concerns seals for use on an aircraft. More particularly, but not exclusively, this invention concerns seals for reducing the aerodynamic drag created by an aerodynamic step, gap or other discontinuity formed between a stationary and moveable element of the aircraft. The invention also concerns an aircraft assembly including such a seal and a method of altering the behaviour of a seal.
In order to reduce the drag generated by a discontinuity in an aircraft surface it is known to arrange a seal to fair (i.e. shield from airflow) or seal (i.e. close off) the discontinuity. For example, a seal blade may be arranged to shield an aerodynamic step, or a seal bulb may be arranged to fill an aerodynamic gap. The performance of a seal at cruise altitude may be of particular interest in view of the time spent by the aircraft at such altitudes. Accordingly, it would be advantageous to provide a seal that gives an improved aerodynamic performance, particularly at cruise altitudes.
Drag reduction using such a seal becomes more difficult when an element defining the discontinuity moves during flight. This may occur when a seal is used with a high-lift device such as a flap or slat or a control surface. In this case, the geometry of the discontinuity may change during flight, and/or the size of any seal may be limited by the need to maintain a minimum clearance so as to allow for the movement of the high-lift device or control surface and/or to prevent the seal becoming entrapped by the high-lift device or control surface. It would be advantageous to provide a seal for use with a moveable element that gives an improved aerodynamic performance and/or reduces the risk of seal entrapment.
FIG. 1 shows an example prior art seal 1 located between a flap 6 on the downstream (right-hand) side and a surface panel 8 on the upstream (left-hand) side. The seal 1 comprises a bulb 2 which appears as a semi-circle when viewed in cross-section in FIG. 1, with the curved portion of the semi-circle on the lower side. A blade 4 extends tangentially rearwards and downwards from the lower edge of the bulb 2. The seal 1 is attached to the rearmost edge of the upstream panel 8 with the body of the seal extending rearwards (towards the right hand side of FIG. 1). A portion of the flap 6 is located in the space above the upper surface of the blade 4 and adjacent the lower surface of the bulb 2.
In use, as the flap 6 is extended and retracted during flight the flap 6 moves relative to panel 8 and seal 1. In flight, as the flap 6 is retracted the front edge of the flap moves closer to and contacts the bulb 2. The force exerted by the flap 6 on the bulb 2 compresses and rotates the bulb 2, said rotation causes the blade 4 to move upwards towards the underside of the flap 6 as the flap moves towards the retracted position. To reduce the risk of the seal 1 becoming trapped between the flap 6 and panel 8, the blade 4 is angled down away from the underside of the flap 4. However, the more the blade 4 is set down from the underside of the bulb 2, the greater the distance between the blade 4 and flap 6 when the flap 6 is retracted, and the less effective the seal 1 is at reducing drag in flight. It would be advantageous to provide a seal that combines a lower entrapment risk with an improved aerodynamic performance.
The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved seal assembly for an aircraft.